Their language, their rules. English is no different. Cows and Bulls, roosters and hens (collectively called chickens), are different words for the same species, but different gender. Lions for both genders, but lioness for female lions, Female horse is a mare, a male is a stallion, etc....
Technically a female cat is a queen and a male cat is a tom.

I re-listened and I could see where someone could mistaken it, especially if they are not used to French, but an easy way to remember is that "fruit" in French is masculine, while mouse is feminine so it would be "le fruit" and "la souris" so you can make out the difference using "le" and "la." I hope that helps :)